Goggle systems for paintball generally consist of a number of items that are over and above normal eye protection. The main requirement of a paintball goggle system is that it protects the user from single or multiple strikes from paintballs that are fired from a paintball marker. Typically, the paintballs are fired at a velocity of 300 feet/second (91.44 m/s) with impact energy of 9.9 foot lbs. (13.42 Joules). For testing purposes, the loads are higher, as specified in ASTM guidelines. The goggle system must perform certain functions: retention on the user's head, maintaining lens integrity to prevent it from popping out under load, and face and ear protection from paintball strikes.
In addition, the ocular chamber is preferably ventilated to allow air to flow across the lens and face to remove condensates. However, due to the nature of the protection required, the venting generally consists of apertures that must prevent a whole paintball or a broken paintball from entering the ocular chamber with sufficient energy to cause eye injury. Another problem with the ventilation is that paintball is played relatively statically, and therefore forced airflow though the goggle is relatively small when compared to skiing, for example, or motocross, or any activity that will provide a ram air effect due to movement. The same problem of a lack of ram air can also occur in these other sports during periods where the wearer is temporarily inactive, such as when the goggle is first put on, or during a break in activity, when it is important that the goggle does not become fogged.
It is a problem with some known goggle systems that the condensation that builds up within the goggle will precipitate onto the lens surface and cause fogging. The key element in this fogging is the dew point of the air, and the fogging can occur in a warm or cold environment, dependent on the relative humidity and the temperature difference between the saturated air and the lens surfaces. Also, in situations where the user generates a high amount of moisture due to sweating, there is little or no airflow present sweating alone can cause fogging.
A number of solutions to the problem of fogging in paintball goggles have been tried and are used, as will now be described.
One known solution to fogging of paintball goggles is to provide an anti-fog moisture-absorbing coating on the inner surface of a single lens. This coating absorbs the moisture that precipitates on the surface, and, in so doing, removes the very small droplets of water that appear as fog on the lens surface, thus maintaining the optical clarity of the lens. However, a disadvantage of this type of coating is that the coating can reach saturation where it will no longer absorb water, and the water can only condense on the lens surface. Once the lens has been in an atmosphere with less humidity, the process will reverse and the moisture will evaporate from the lens coating. Further problems with this type of coating are that the coating has a limited use in relation to the amount of moisture it can absorb; the coating itself is very fragile and prone to scratching or marking; and, should, the coating become damaged, its optical properties and anti-fogging properties are substantially reduced.
Another solution is the use of double lenses, which generate a thermal barrier within the lens structure working on the same principle as double-glazing. The inner lens surface is warmer than the outer lens, and, because the inner lens remains warm, the moisture-laden air will not condense onto the lens surface to cause fogging. A problem with double lenses is that the lenses must remain hermetically sealed to prevent any moisture from entering between them, or condensation will form between the lenses. Another problem that can be associated with double lenses is that the lens structure becomes thicker and, due to its relatively close proximity to the eyes, a distortion can occur causing parallax, which affects the optical properties of the lens.
Some manufacturers have attempted to insert fans within the goggle system in the brow area of the goggle; these are successful to a degree. However, these systems have not provided a completely satisfactory solution to the problem of fogging, and fan-assisted goggles have often required that they be backed up with anti-fog or thermal lenses to ensure adequate performance.